/*
	Name: 1_1
	Copyright:Take it at will
	Author:Rodney
	Date: 
	Description:
*/
#include<stdio.h>
#include<stdlib.h>
#include<math.h>


int main()
{
	double mid,x=0.5,epsilon=1E-6;
	double jc=1.0,s=x;
	int i,tag;
	for(i=1,tag=1;;i++)
	{
		tag*=-1;
		jc*=i;
		mid = pow(x,2*i+1)/((2*i+1)*jc);
		if(mid < epsilon)
			break;
		s+=tag*mid;
	}
	
	printf("%lf\n",s);
}

